Apple watch series 3 GPS only

No.

You need an iPhone 6s, SE, 7, or newer.

The Apple Watch is an iPhone accessory, not a standalone device.

A GPS model is very useful if you generally have your iPhone with you or somewhere in the house. The cellular model is useful to people that either like to leave their iPhone at home, or often forget their iPhone, but still want phone calls, messages, etc...

It will work to some extent.

You still need an iPhone to set it up, however it will work in a limited capacity after being set up, if the paired iPhone is not nearby.

See here: Use your Apple Watch without your iPhone nearby - Apple Support